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The Waters of the Nile

Bridget Gleeson

September 1, 2002

The Waters of the Nile

Jeffrey Mathison

As the sun sets, a donkey gazes at its reflection in the calm waters of the longest river in the world. Upstream, a young woman in a bright red dress crouches beneath a dusty palm tree, washing pots and pans in the cool blue water. A scorpion hides beneath a clump of lotus flowers as a white-haired man steps into the river to bathe.

Several miles up the Nile, a child chases a dog among the clusters of mud-brick buildings that border the western bank. This town, Edfu, is home to Horus Temple—the largest and best-preserved temple in all of Egypt. Completed in 57 BCE, the sprawling temple and its grounds hosted crowds of Egyptians for feasts and celebrations in honor of Horus, the falcon god of the sky. By day, tourists from around the world visit Edfu to view the numerous chapels and cult areas devoted to Egyptian gods and goddesses. Now, as night falls, the stragglers have retreated to their river boats, and the air is quiet except for the faint sound of moving water.

The next morning, about 30 kilometers northwest of Edfu, the sun rises at Hierakonpolis. Dirt roads lined with shabby houses lead to the site of an important yet little-known ancient temple. Like Edfu, Hierakonpolis was a major cult center for the worship of the god Horus; in fact, Hierakonpolis means "city of the falcon" in Greek. But Hierakonpolis is much older than Edfu, inhabited since 3800 BCE. By 3500 BCE, the desert town was bustling with human life. Ancient Egyptians worshipped at the temple, fired pottery on a vast system of kilns, and even produced beer at a primitive brewery. Artifacts from this period, including the famous Narmer Palette, an elaborately engraved stone tablet depicting events in Egyptian history, suggest that Hierakonpolis was actually the first capital of a unified Upper and Lower Egypt, where the earliest pharaohs lived. But today no guidebook-toting tourists are seen wandering around the ruins. Instead, a small group of American archeologists, geologists, and hydrogeologists are scattered across the site. Garth Llewellyn, an outdoorsy-looking geosciences student with stubble on his chin and dust on his hiking boots, is getting ready to dig a hole.

Jeffrey Mathison

Since 1897, when British Egyptologists James E. Quibell and Frederick W. Green first excavated Hierakonpolis, archaeologists have continued to carefully uncover the ancient remains. The early British explorers were mainly interested in extracting valuable treasures, such as the solid gold head of Horus statue that now sits behind glass at a museum in Cairo. More archeologists investigated the site throughout the 20th century; most notably, Walter Fairservis of Vassar College, who started an ongoing excavation in 1967. Elizabeth Walters, professor of art history at Penn State, worked on the site with Fairservis, and took over the project when he died in 1994.

The site still consists of three mounds—the main temple and two outlying structures that were probably inhabited by people. Visitors can only see the tops of dusty mud-brick walls emerging from the earth. "Basically, it looks like a field with buried walls," Llewellyn says. Thousands of years have buried the structures in the ground, leaving modern archeologists with much to uncover. Currently, though, the dig is at a standstill due to a rising local water table caused mainly by irrigation of the surrounding farmlands. Four years ago, Walters contacted Penn State geosciences professors Shelton Alexander, David Gold, and Richard Parizek for help. They initiated the Temple-Town Hierakonpolis Project, with the goal of "dewatering" the site. Since then, the team has traveled to Hierakonpolis annually for about three weeks at a time to work on the project. Last year, in need of a senior thesis topic, Llewellyn accepted Alexander's invitation to go to Hierakonpolis for three weeks in January 2001 to help collect field data.

Archeologists cannot dig in soggy soil, so the team working at Hierakonpolis must first focus on hydrogeology. "Hydrogeology is important for many reasons," Llewellyn says. "We need to understand how our environment interacts with water to help prevent the degradation of one of our most important natural resources. In industrialized areas, such as central New Jersey, contamination of groundwater is always a concern. Also, water isn't always abundant. Arid regions of the world, like Egypt, depend on very limited supplies of water. Already, the United States is experiencing difficulties in many areas providing clean and abundant water. Hydrogeology is a science that helps to provide solutions for these problems."

The top layer of earth at Hierakonpolis, about a meter thick, is mostly dry sand and silt. The next layer, predominantly dark clay, is about half as thick, and contains pottery shards and charcoal, evidence of human occupation. The lowest layer, about two meters beneath the surface, is mainly yellow clay. The foundations of the ancient structures of Hierakonpolis are estimated to be another two meters down.

As with most materials, Llewellyn explains, these strata have pores that allow water to filter through. Typically, a completely water-saturated zone exists at some depth; the surface of this zone is called the water table. At Hierakonpolis, the nearby Nile River has always contributed to the water table. Lately, additional local sources of water have added to the water table as well. Sugar cane grows in the land surrounding the archeological site, sustained by irrigation from a network of canals. With increased agricultural development over the past century, the local water table has slowly risen. As Alexander explains, the earliest excavators at Hierakonpolis observed that the water table had risen within about 4 meters of the surface. "By the time Fairservis was excavating in the late 1960s," he says, "the water table was starting to become a problem. The groundwater had risen to a little more than 2 meters below the surface. Since then, the water table has continued to rise, and now it is between 1 and 2 meters beneath the surface at the site. And we don't know exactly what all the water sources are. There could also be underground aquifers feeding into that area underneath the site, contributing to the water problems. We're not really sure yet."

Major problems for excavation are created by the rising water table. As Llewellyn says, "The soil beneath the surface is basically composed of very fine sand and silt, so when the soil is saturated with water, we can have quicksand conditions. Obviously, we can't continue with the dig when we have quicksand." In addition, quicksand conditions can damage the stratigraphy of the site. "Stratigraphy is like a footprint in time. Archeologists excavate at small intervals in depth in order to date the items they uncover. There are distinct layers of soil and rock, and each has unique characteristics. You might find strata that have some type of pottery not found in other sections—this tells you something about the age of that particular level. When you attempt to excavate in saturated conditions, strata begin to mix. That is very bad for archeology." The salt content in the water also presents a problem, because structures or artifacts deteriorate more quickly when exposed to salt.

Archeologists often must work around water. At an excavation in Washington, D.C., for example, geologists used a "sump pump" to remove water that was seeping up into the site. But according to Llewellyn, that method is not practical for Hierakonpolis. "Oftentimes, a sump pump will be used to dewater an area. We could dig a ditch at a lower elevation than the site, and let the water flow down into it. Then we could use a sump pump to remove the water from the ditch. But in this situation, a sump pump is not the answer. For one thing, it is too expensive to use for extended periods of time. We want a solution to our water problem that will last indefinitely, while remaining cost-efficient."

Jeffrey Mathison

Hierakonpolis, once a bustling Egyptian village, now lies beneath layers of dust. Irrigation of surrounding farmlands poses a threat to the site's excavation: The earth's layers provide archeologists with a natural time stamp; a rising water table could mix the strata, making artifact dating difficult."

By gathering as much information as possible, the team can eventually develop an efficient plan. Llewellyn's main task while at Hierakonpolis was to collect information about the conditions of the shallow layer of earth above the water table. "It is important to characterize the entire site prior to developing a dewatering scheme. We must know what problems we might encounter," he explains.

In December 2000, for example, Alexander installed an array of small sensors called geophones into the earth to record seismic waves. Then, he poked a hole about 5 centimeters wide and a meter deep in the ground and inserted a metal "firing pin." At the buried tip of the firing pin was a small gun called a "Betsy Seisgun." The "Betsy Seisgun" held a shotgun shell at the end that Alexander lowered into a shallow shot hole. When he tapped a hammer at the top of the firing pin, the seismograph started recording and the Seisgun fired the shotgun shell, sending sudden impulses into the ground. The energy traveled through the ground and was detected by the geophones in the form of seismic waves. The seismic information is stored digitally and is also displayed as a series of squiggly lines on the seismograph's small screen. By analyzing the recorded signals, Alexander could measure the velocity of the seismic waves and look for anomalies. Llewellyn looks over printed versions of these readings, pointing out an area where the squiggly lines have larger amplitudes. "That," he says, "is an anomaly."

Alexander's studies of Hierakonpolis in January 2000 showed unusually high-frequency seismic waves—an anomaly—located above the water table at a depth of less than 1 meter. Whereas the seismic waves traveled through layers of dry soil and silt with an average velocity of 130 meters per second, these anomalous waves traveled with a velocity of about 1500 meters per second. Since seismic waves travel more quickly through water-saturated sediments, the contrast in Alexander's study suggested that one or more thin layers of water-saturated material were the cause of this shallow anomaly. The actual water table could account for strong, later-arriving high-frequency signals, but not these anomalous high-frequency early signals. The study left Alexander with some questions. Did another very shallow, water-saturated layer above the water table exist beneath the surface? Or was water perched on top of buried, man-made structures?

Llewellyn squints into the sun. Although it is January, the temperature has hit 70 degrees today at Hierakonpolis. The team is spread out across the site, poking instruments into the soil and recording measurements in notebooks. A handful of Egyptians from the local village have been hired to assist the scientists with manual labor, such as digging trenches. In this remote, poverty-stricken region, helping out the Penn State scientists at Hierakonpolis is a lucrative way to spend the day.

Today, Llewellyn is digging water holes to investigate the cause of the shallow seismic anomaly and to measure the depth of the water table. Instead of using seismic refraction, he is using an auger to create water holes, so the water level can be measured from inside the hole. "If the seismic data interpretation is correct," he says, "the water table elevations should correlate."

Llewellyn is preparing to dig his first hole of the day. He takes care to choose an appropriate location. Each day, he has drilled about three holes near the locations where the shallow seismic anomalies were detected. He needs to dig as many holes as possible to help him understand the anomaly, because the water table is not flat and has risen to different levels. The water that flows beneath and around the ancient structures can be obstructed by impermeable barriers, such as temple walls. Flowing groundwater that meets a mud-brick wall will move around it, rising higher while the water level within the walls stays lower. Also, if a canal is feeding into the water table, then the areas closer to the source will rise to a higher level before the areas further from the source are affected. These variations in the water table necessitate measurements at a number of different locations.

Having chosen his spot, Llewellyn drills a hole about 18 centimeters wide, going down until he hits the water table—usually around 1.5 to 3 meters in depth. Setting aside the drill, he peers into the dark hole to see the small puddle at the bottom. He inserts into the hole a device known as a piezometer. The piezometer is a narrow pipe with a short screen at the bottom that lets in water. Llewellyn can determine the water table level by reading the height to which the water rises. These holes are also used to measure water temperature, which is helpful in determining the flow system and the permeability of strata. Llewellyn leaves the piezometers in the holes so they can be used later to collect more data. While finishing with a hole, Llewellyn carefully samples the sediments and other materials at specific levels. He places these materials in bags and carefully marks the level in the hole from which it came. Later, Parizek and Llewellyn closely examine the bags' contents to create a detailed log of what materials are present at what depths. They also look for pottery shards and other materials that can be dated, and could help to estimate the age of a certain stratum.

Later, Llewellyn tried to match the actual elevation of the water table with the predicted levels obtained through seismic refraction. Although some measurements did not correlate well, the correlations from the anomalous layers were fairly successful. Any discrepancies between the seismic data and the water table elevations Llewellyn recorded were probably due to varying groundwater levels and human error.

Jeffrey Mathison

Another significant result of Llewellyn's work was that clay-rich silt and sand was discovered in the holes. Because clay is virtually impermeable—water can not travel through it—these materials had formed a boundary between the ground surface and the water table. This layer of impermeable sediment had trapped water above the water table. "This is known as a perched water condition," Llewellyn explains. "In Egypt, this can only occur by two means. There can either be lateral groundwater movement along the clay-rich stratum, or the water table rose above the clay layer and then fell, leaving perched water." Alexander's seismic data from January 2000 indicated a high-frequency anomaly that could have been caused by a water-saturated layer between the water table and the surface. Llewellyn's and Parizek's discovery of clay in the holes suggests that, in fact, an impermeable boundary composed of clay-rich silts and sands was causing the high-frequency, high-velocity seismic anomaly. The alternative of a perched zone above a man-made structure was ruled out.

Llewellyn's research is only one contribution in a large effort to characterize the entire site—like one piece of a large puzzle. Alexander, Parizek, and Gold continue to collect seismic and hydrogeologic information about the site in order to develop an efficient scheme for dewatering Hierakonpolis. When the team figures out how to lower the water table, archeologists all over the world will possibly benefit. The nearby Horus Temple in Edfu, for example, is also facing a hydrogeological crisis far beneath the feet of tourists. Because the ancient Egyptians rebuilt their towns by constructing new structures on top of old debris, the foundations of Horus Temple are buried deep in the ground. Salt water is being absorbed into the temple walls, accelerating the temple's deterioration. If the team working at Hierakonpolis can figure out a way to dewater the site, similar hydrogeological methods could be applied at the Horus Temple.

According to Alexander, the team should soon have a solution. He and the other project leaders receive bimonthly reports from Hierakonpolis. The Egyptian Geological Survey team checks the piezometers and the borehole temperatures and salinity periodically, sending them to the Penn State professors for analysis. Sitting in a lecture room on campus, Alexander pores over a stack of charts and discusses future plans. "We may try to continuously pump the water out, using wells or another power source," he says. As Llewellyn had mentioned, a sump pump uses too much electricity and is too expensive, but some sort of pump might work. "In the future," Alexander predicts, "we will most likely carry out an experiment to show that using a pump is a feasible way to allow excavation in the future. We are currently receiving funding to drill exploration holes in different locations at the site and around the surrounding area to find out where the water is coming from."

The team will be returning to the site for a few weeks in May 2002 to drill and sample several deeper holes, working in collaboration with the Egyptian survey. In 1997, the first year Alexander worked at Hierakonpolis, his seismic surveys indicated what seems to be a buried channel of the Nile 100 meters beneath the site, as well as a possible water aquifer 30 meters down. The Penn State team plans to drill holes through these areas in the future, because this water source could be contributing to the hydrogeological problem near the surface. "From all these observations, we are just trying to come up with a viable strategy for dealing with the water problem at Hierakonpolis," Alexander says. "I think we're getting pretty close to putting together a picture of the hydrogeological system."

When the team returns to Egypt in May, Llewellyn will not be with them. But as a first-year graduate student at Penn State, he is focusing on hydrogeology. His experience at Hierakonpolis only intensified his interest in the subject. Working with professors trained in different disciplines taught him the importance of a wide-ranging education. "I want to be well-rounded," he says. "I don't want to specialize too much. Geophysics and other disciplines can be used collaboratively with hydrogeology. Having knowledge of these subjects is useful for future studies—different circumstances require different expertise."

Somewhere across the world, a geologist is scribbling numbers in her notebook as the sun sets over Hierakonpolis. A weary Egyptian quits for the day, gulping from his water bottle and leaving the field with a bundle of sugar cane strapped to his back. Water is the center of life in Egypt, where people use the Nile for everything from washing laundry to transporting goods. Though foreigners might idealize Egyptian culture, envisioning only the glamorous pharaohs and pyramids, Llewellyn knows better. His experience at Hierakonpolis revealed to him the reality of today's culture, causing him to think differently about both Egypt and his own homeland.

"People take water for granted here. They think, well, every time I go to the water fountain, I have water to drink, so what's there to worry about? And then they go about their daily business. Not everyone is as fortunate as we are. That is one thing I learned in Egypt."

Garth Llewellyn received a B.S. in geosciences in December 2001 from the College of Earth and Mineral Sciences. His adviser was Shelton S. Alexander,Ph.D., professor of geophysics, 537 Deike Bldg., University Park, PA 16802; 814-863-7246; ssa2@psu.edu. The Temple-Town Hierakonpolis Project is led by a team consisting of Elizabeth J. Walters, Ph.D., associate professor of art history;David P.Gold, Ph.D., professor emeritus of geology;Richard Parizek, Ph.D., professor of geosciences and geoenvironmental engineering; and Alexander. The project is funded by the College of Earth and Mineral Sciences, the University's Dean for Undergraduate Education, external private sources, and a joint U.S.-Egyptian grant administered through the National Science Foundation.